1. Field of the Invention
This invention relates to an apparatus and method for processing piezoelectric elements, quartz resonators and other resonant elements while monitoring and regulating the resonance frequencies of the elements, piezoelectric elements produced by such apparatus and method, and resonators and related devices using such elements.
2. Description of Related Art
In a generally recognized frequency adjustment method for the regulation of the frequency of piezoelectric elements in quartz resonators, deposition is done through a mask during manufacture in order to directly obtain the desired frequency. Alternatively, in recent years, sputter-etching and ion beam radiation with an ion gun has been used to remove material from an electrode in order to obtain the desired resonance frequency, in a so-called plasma frequency adjustment method.
According to a frequency adjustment method using a plasma, initially a specified amount of the piezoelectric parent material is cut out, forming an angular cut, following which it is polished, to finish the piezoelectric form. Following the alignment of a mask patterned after the shape of the electrode to one surface of the piezoelectric form, a silver metallic film is deposited in a vacuum, thereby forming the base electrode. Unlike the frequency adjustment method of deposition accomplished under the related art, the frequency is controlled during deposition by monitoring the film thickness so that the resonance frequency can be set 500-2000 ppm lower than the desired resonance frequency.
The manufacture results in the film thickness being greater than that of the electrode film thickness for the desired resonance frequency.
The piezoelectric element which is provided with an electrode formed in the manner described is mounted in an appropriate holder, and through the application of sputter-etching or ion beam radiation, the thickness of the electrode is reduced by removal of material from an electrode, thereby increasing the resonance frequency, in order to obtain the desired resonance frequency. When accomplishing the regulation of frequency in the manner described, initially the resonance frequency of the piezoelectric element is measured to determine how far the resonance frequency differs from the desired final resonance frequency. The processing rate for accomplishing the frequency adjustment of the piezoelectric element is established on the basis of the measured sputter-etching or the intensity of the ion beam, and the sputter-etching or ion beam radiation time can be determined for various processing rates and frequency differences from the desired resonance frequency.
Next, radiation is commenced on the basis of the determined rates and times. The measurement system cannot be used effectively because there is a direct flow of electric current on the piezoelectric element. Therefore, before the full radiation time is completed, the radiation is cut off, the electrical system is reconnected, and the resonance frequency of the piezoelectric element is measured to determine the resonance frequency and the difference from the desired resonance frequency. Through repetition of this operation, the frequency difference may be reduced to nearly zero.
With the related art frequency adjustment method in which use is made of deposition directly to make the frequency adjustment, it is essential that a slow deposition process be used. Furthermore, it is essential that the mask used to restrict the portion of deposition be one of high precision, which is extremely costly in equipment and operational time. In addition, the accuracy of the frequency adjustment has not been very high. In contrast, with the frequency adjustment method in which use has been made of plasma, the operational time is shortened, reducing production costs, and there is the added benefit that the frequency adjustment is also more precise.
However, even with the frequency adjustment method using a plasma, there are a number of problems which need to be resolved. First of all, since a direct electric current flows on the piezoelectric element or other workpiece, the resonance frequency during the adjustment of the frequency has not been able to be monitored. Because of this, the radiation time has been established from the processing rate, and there has been no alternative except to adjust the frequency by controlling this time.
The processing rate which determines the radiation time can be calculated based on the size of the electrode and a number of other factors. However, even with the same frequency band, there will be individual differences in processing the various piezoelectric elements. In addition, there are a number of processing factors which affect the processing rate, such as the stability of the sputter gun or the ion beam gun source, and the atmosphere of the processing device. Also, it is very difficult to coordinate and to control those factors. Thus, if control is exercised only over the radiation time, the resonance frequency following the frequency adjustment will deviate from the desired resonance frequency. Therefore, the radiation time is divided by frequency measurements and adjustments of the radiation time are made in coordination with the resonance frequency measurements. Since it is necessary to repeat such steps as radiation, frequency measurement, etc. many times, shortening of the processing time is not effectively accomplished. In addition, since the radiation is continuously operated in order to assure a high degree of accuracy and the coordination of the final frequency, a high degree of experience is necessary to operate the processing device, making it difficult to automate.
There is also the problem of the processing rate. If the voltage and electrical current are impressed on the sputtering gun or ion gun in a fixed manner, then the radiation is of a fixed energy, and the processing rate also is maintained in a roughly fixed state. However, when there is a great difference between the desired resonance frequency of the workpiece and the measured frequency, then if a large processing rate is not obtained, the processing time becomes extended, and there is a deterioration in the manufacturing efficiency. On the other hand, when minute adjustments in the resonance frequency are needed, if the processing rate is not small, then there will not be a great deal of precision in the adjustment. A certain amount of precision can be assured through increasing the processing rate and using a shutter mechanism and the like. However, the processing device becomes complicated, and consideration needs to be given to a number of problems relating to its control and stability of operation. In addition, even if such mechanisms are used, a great improvement in the precision of the frequency is not expected.
By controlling the supply of electric current to the radiation source such as, for example, the ion gun, it is also possible to adjust the processing rate. However, if the processing rate is changed, then there is also a change in the processing time, and if there is not precise control of the energy of the ionized atoms, then the processing time cannot be established with a high degree of accuracy. Furthermore, it will also be difficult to monitor the resonance frequency, and even if the processing rate could be changed and the processing time shortened, ultimately it will be difficult to assure the accuracy of the frequency. In addition, in order to maintain the constant radiation emission from the radiation source, it may be necessary to supply electric power in greater than a fixed level, as well as to resolve instabilities in the radiation source originating in changes in electric power.
Through the use of a plasma, the method for frequency adjustment by reduction in the thickness of the electrode appears capable of a great improvement in precision with a shortening of the processing time. However, products with stable performance at low cost have not been achieved.